The principal of electrostatic attraction has been used for many years to enhance the removal of contaminants from air streams. There are three primary categories of air electrostatic cleaners: electrostatic precipitators, passive electrostatic filters and active field polarized media air cleaners, which are sometimes known under different terms.
Electrostatic precipitators charge particles and then capture them on oppositely charged and/or grounded collection plates.
A passive electrostatic filter (also know as an electret) employs a media (or combination of different media) that through some combination of treatment and/or inherent properties has an electrostatic charge. Particles entering the filter media that have an electrostatic charge are attracted to the charged media filter materials that have the opposite electrostatic charge.
An active field polarized media air cleaner uses an electrostatic field created by a voltage differential between two electrodes. A dielectric filter media is placed in the electrostatic field between the two electrodes. A dielectric material is an electrical insulator or a substance that is highly resistant to electric current that can also store electrical energy. A dielectric material tends to concentrate an applied electric field within itself and is thus an efficient supporter of electrostatic fields. The electrostatic field polarizes both the media fibers and the particles that enter, thereby increasing the efficiency of the media and the air cleaner. The efficiency of the filter is the percentage of particles removed from the air stream at a given particle size, or for a range of particle sizes.
A further electrostatic air filter design is disclosed in Canadian Patent No. 1,272,453, in which a disposable rectangular cartridge is connected to a high voltage power supply. The cartridge consists of a conductive inner center screen, which is sandwiched between two layers of a dielectric fibrous material (either plastic or glass). The two dielectric layers are, in turn, further sandwiched between two outer screens of conductive material. The conductive inner center screen is raised to a high voltage, thereby creating an electrostatic field between the conductive inner center screen and the two conductive outer screens that are kept at an opposite or ground potential. The high voltage electrostatic field polarizes the fibers of the two dielectric layers.
The air cleaners may be installed in a variety of configurations and situations, both as part of a heating ventilating and air conditioning (HVAC) system and in standalone air moving/cleaning systems. In smaller HVAC systems (e.g. residential and light commercial), the air cleaner panels are often installed in a flat configuration (perpendicular to the airflow) or in angled filter tracks. In larger systems, banks of air filters are typically arranged in a V-bank configuration where multiple separate filters are positioned to form a Z-fold filter perpendicular to the axis of airflow.